1. Field of the Invention
Phosphate fertilizers are very important in the agricultural economy throughout the world. A principal phosphate source for such fertilizers is natural phosphate rock which, in its natural form, is nearly insoluble in water. To utilize phosphate from natural phosphate rock sources, various acidulation processes have been used to solubilize the phosphates. This invention provides for solubilization of phosphate rock by contacting the rock with an aqueous solution of sulfurous acid in the presence of an oxidizing agent of hydrogen peroxide.
2. Description of the Prior Art
Processes for phosphate fertilizer production utilizing sulfur oxides obtained from flue gas of combustion of sulfur containing fossil fuels, such as coal or oil, or sulfur oxides obtained as stack gas effluents from any industrial plant such as chemical, paper, refinery, fertilizer, steel or coke operations, in the production of phosphate fertilizers is known from U.S. Pat. Nos. 4,073,634, 4,168,150, and 4,252,553. These patents and the patents cited therein are incorporated herein by reference for their teachings regrading solubilization of phosphate rock by the use of sulfur oxides. The above cited patents teach that when untreated phosphate rock is used, the sulfur containing acid must be predominately sulfuric acid to obtain the desired high phosphate solubility from the phosphate rock. However, when utilizing sulfur oxides derived from glue gas, it is necessary to further oxidize the sulfur oxides to obtain the necessary amount of sulfuric acid. This problem becomes greater with increased amounts of sulfur in the fuel. U.S. Pat. No. 4,252,553 teaches that thermally pretreated defluorinated fluorapatite has been found to react with a sulfur containing acid which is predominately sulfurous acid formed by the reaction of a sulfur oxide containing gas with water, thus alleviating the necessity for further oxidation to sulfuric acid to obtain high solubilization of phosphate rock.